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w- <br /> -sr <br /> L <br /> . �-� �a�:orato Procedures <br /> All of the samples collected during the field phase of the <br /> survey were analyzed according to EPA Method 602 on a gas chromato-. <br /> graph equipped with a flame ionization detector (GC/FID) , but using <br /> direct injection instead of purge and trap. Analytes selected for <br /> standardization were: <br /> methyl tertiary butyl ether (MTBE) <br /> benzene <br /> toluene <br /> ethylbenzene <br /> meta- and para- xylene <br /> ortho-xylene <br /> t <br /> /These compounds were chosen because of their utility in evaluating <br /> the presence of petroleum products such as fuels, lubricating oils, <br /> and non-halogenated solvents. <br /> FID Total ;Volatiles values were generated by summing the areas <br /> of all integrated chromatogram peaks and calcu"ating using the in- <br /> strument response factor for toluene. Injection peaks, which also <br /> contain the light hydrocarbon methane, were excluded to avoid the <br /> skewing of Total VolatiXes values due to injection, disturbances <br /> and biogenic methane. r <br /> z The analytical equipment was calibrated using an instrument- <br /> response curve and injection of known concentrations of the above <br /> standards. Retention tim4s of the standards were used to identify <br /> the peaks in the chromatograms of f the field samples, . and their <br /> response factors were used to calculate the analyte concentrations. <br /> - The tabulated results of the laboratory analysis of the soil gas l <br /> samples are reported in micrograms per liter (ug/1) in Table 1. <br /> Map sample points with no data shown indicate that the analyte <br /> concentrations in the samples were below the detection limit. <br /> 5 <br />